Well there's two things to that. Nova knives were made because of the martial traditions of the Raata empire (that later became the caldari state) and minmatar use them for a few reasons 1) there's parallels within their own tribal societies. 2) minmatar are outside the box thinkers that will do almost anything if their hand is forced. 3) Minmatar favor reliable, conventionally low-tech solutions to problems. 4) The Ishukone corporation (which are caldari liberals) have an incredibly strong relationship with the minmatar - having previously given extremely large quantities of insorum for free to the minmatar republic, insorum is the cure to the previously thought 'uncurable' vitoc 'poison/mutagen' used by the amarr to control minmatar slaves. Ishukone make nova knives and SMG's for the minmatar at extremely low costs because of that relationship and the forward looking mentality of the liberals.



Caldari racial doctrine is 'siege warfare' this is what their gang links and command ships get bonuses to in eve. This is represented in dust best by nanohives, injectors and incredibly long range weaponry - the caldari take a position, fortify it and bombard you with long range weapons until you submit, when they advance someone covers them. Snipers fit this as it's a very patient and stationary playstyle that fits the caldari methodology. Hell in space caldari fleets tend to drop out of warp at 200km, the admiral lights his cigar and then missiles and rails start firing at everything - if something gets close the caldari either warp off & back in or activate micro jump drives and move 100km away.

Gallente racial doctrine is 'information warfare' this is what their gang links and command ships get bonuses to in eve. This is represented relatively well in dust by their scanners and scouts - they see you, you don't see them. They then use this information to pick off high value targets and move in with their preferred short range blasters to brawl at short range. Snipers tentatively fit information warfare in theory, but with the gallente's heavy preference for short range engagements of high armor / mobility superiority it's unfeasible.

Amarr racial doctrine is 'armored warfare' this is what their gang links and command ships get bonuses to in eve. It's hard to say this is particularly well represented in dust simply due to lack of amarr content, but in general amarr engage at medium to long range with suits that just don't ****ing die. They're not afraid of getting up close and should any individual actually drop they can immediately come back due to the short reinforcement lines provided by drop uplinks. Furthermore war to the Amarr is incredibly psychological, they have a high preference for visibility and visibly breaking their opponents will either through the belief of 'IT WILL NOT DIE" presented in their sentinels or weapons that you go "Oh god, that thing just killed four people with one sweep of his laser". In fact the laser rifle is incredibly psychological everyone knows what pre-heated lasers do to any suit and they'll frantically scramble to find cover if a laser is trained on them. The Amarr want you to know what killed you and where it was.

Minmatar racial doctrine is 'skirmish warfare' this is what their gang links and command ships get bonuses to in eve. Plain and simple, Minmatar are a blitzkrieg on legs. They come in lightning fast with explosions, walls of bullets, loud noises and before you know it it's all over everyone is dead from knives, bullets, grenades or other explosions. They're relatively versatile and pragmatic in their loadouts, but the patience and immobility a sniper requires in no way fits the minmatar doctrine as they operate entirely on shock and awe.

In short the sniper rifle is a specialty weapon that only really fits the long range & patient style of the caldari, other races would have entirely unique 'long range' specialist weapons. Variant weapons are created largely to go 'This is what this weapon would be if x race designed it or commissioned it for use within a different army' which is why I'd be okay with renaming a few sniper rifles but not okay with just doing an oprah "EVERYONE GETS A SNIPER/SHOTGUN/KNIFE!".

How does the Rhoden sniper rifle fit in? And wasn't there a minmatar variant already in the making, but never published?